Battery Management System For Control Of Lithium Power Cells

ABSTRACT

An intelligent rechargeable battery pack having a battery management system for monitoring and controlling the charging and discharging of the battery pack is described. The battery management system includes primary and secondary protection circuits for monitoring the charging and discharging of the battery. Individual battery cells forming the battery pack are connected by a main bus to a connector for connection to a battery charger or a device to be powered, and the main bus may be interrupted by a switch controlled by the battery management system to prevent damage to the battery during charging or discharging of the battery.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/458,952, filed Apr. 27, 2012, now U.S. Pat. No. 9,299,877, issuedAug. 4, 2015, and claims the benefit of priority to U.S. ProvisionalApplication No. 61/522,192, filed Aug. 10, 2011 and U.S. ProvisionalApplication No. 61/480,286, filed Apr. 28, 2011, and to all of thepatents and applications in the chain, all of which are incorporatedherein in their entireties by reference.

This application is related to U.S. application Ser. No. ______,entitled “Latch Mechanism For Battery Retention,” filed ______; U.S.application Ser. No. ______, entitled “Battery Management System WithMOSFET Boost System,” filed ______; U.S. application Ser. No. ______,entitled “System and Method For Automatic Detection Of BatteryInsertion,” filed ______; U.S. application Ser. No. ______, entitled“System and Method For Tracking And Archiving Battery Performance Data,”filed ______; U.S. application Ser. No. ______, entitled “ViralDistribution of Data, Operating Parameters and Software Using A BatteryAs A Carrier,” filed ______, the entireties of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The invention is directed to a battery pack for providing power to adevice. More specifically, the invention is directed a battery pack andbattery management system for managing the charging and discharging ofthe battery pack so as to maximize the amount of power available fromthe device when in use and to recharge the battery in a manner as toprolong the useable life of the battery.

BACKGROUND OF THE INVENTION

Cardiopulmonary resuscitation (CPR) is a well-known and valuable methodof first aid used to resuscitate people who have suffered from cardiacarrest. CPR requires repetitive chest compressions to squeeze the heartand the thoracic cavity to pump blood through the body. Artificialrespiration, such as mouth-to-mouth breathing or a bag mask apparatus,is used to supply air to the lungs. When a first aid provider performsmanual chest compression effectively, blood flow in the body is about25% to 30% of normal blood flow. However, even experienced paramedicscannot maintain adequate chest compressions for more than a few minutes.Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26Ann. Emerg. Med. 300 (September 1995). Thus, CPR is not often successfulat sustaining or reviving the patient. Nevertheless, if chestcompressions could be adequately maintained, then cardiac arrest victimscould be sustained for extended periods of time. Occasional reports ofextended CPR efforts (45 to 90 minutes) have been reported, with thevictims eventually being saved by coronary bypass surgery. See Tovar, etal., Successful Myocardial Revascularization and Neurologic Recovery, 22Texas Heart J. 271 (1995).

In efforts to provide better blood flow and increase the effectivenessof bystander resuscitation efforts, various mechanical devices have beenproposed for performing CPR. In one variation of such devices, a belt isplaced around the patient's chest and an automatic chest compressiondevice tightens the belt to effect chest compressions. Our own patents,Mollenauer et al., Resuscitation device having a motor driven belt toconstrict/compress the chest, U.S. Pat. No. 6,142,962 (Nov. 7, 2000);Bystrom et al., Resuscitation and alert system, U.S. Pat. No. 6,090,056(Jul. 18, 2000); Sherman et al., Modular CPR assist device, U.S. Pat.No. 6,066,106 (May 23, 2000); and Sherman et al., Modular CPR assistdevice, U.S. Pat. No. 6,398,745 (Jun. 4, 2002); and our application Ser.No. 09/866,377 filed on May 25, 2001, our application Ser. No.10/192,771, filed Jul. 10, 2002 and our application Ser. No. 12/726,262,filed Mar. 17, 2010 show chest compression devices that compress apatient's chest with a belt. Each of these patents or applications ishereby incorporated by reference in their entireties.

Since seconds count during an emergency, any CPR device should be easyto use and facilitate rapid deployment of the device on the patient. Ourown devices are easy to deploy quickly and may significantly increasethe patient's chances of survival.

One important aspect of such devices is the need for small, powerful yetreliable power supply to power the device. However, such a need is notlimited to mechanical compression devices such as those described above.There are many medical devices which require a light weight powersupply, typically a battery, which must be capable of deliveringsufficient energy to the device for an extended period of time.Moreover, the power supply must be relatively light weight, so as toenhance portability of the medical device, yet it must deliver its powerfor an extended period of time without significant voltage or currentdrop off to ensure consistency of operation throughout the period thedevice is being used.

Modern batteries typically require additional electronic circuitry or abattery management system designed to manage the operation of thebattery. Such a battery management system should be able to monitor theoperation of the battery, including charging and discharging of thebattery without significantly adding to the internal resistance of thebattery. Moreover, a battery management system should also be capable ofaccommodating different battery chemistries as battery technologyevolves. To accomplish this, the battery management system will alsoneed to have sufficient processing power and memory capacity to recordevents that occur during the lifetime of the battery, and to be able toanalyze and/or communicate data related to those events to a centralizedor distributed server system for analysis. The battery management systemwill also include various safety related systems designed to protect thebattery, the devices being powered by the battery, and users of thebattery or powered device from various environmental or operationalfactors that may occur. The present invention satisfies these, and otherneeds.

SUMMARY OF THE INVENTION

In a most general aspect, the invention provides a high-performancebattery pack capable of reliably providing high power and current topower a device for a prolonged period of time. Moreover, the batterypack includes a battery management system that monitors and controls allaspects of battery operation, including charging and discharging of thebattery. The battery management system is also capable of recordingevents that occur during charging and discharging of the battery pack,and communicating those events for later analysis. The batterymanagement system is further capable of being updated with enhanced orimproved operating parameters, and is capable of managing variousbattery chemistries to provide for forward and backwards compatibility.

In one aspect, the battery management system of the present inventionincludes a circuit that monitors the charging of each cell of thebattery pack to prevent voltage imbalances between cells. A bleedcircuit is included that is configured to bleed off excess charge fromeach individual cell.

In another aspect, the battery management system includes a primaryprotection circuit that monitors the charging and discharging of eachbattery cell in the battery pack. If a fault is observed, the primaryprotection circuit provides a signal that drives the gate of one or moren-FET devices to open a main bus of the battery to interrupt currentflow from the battery.

In still another aspect, the battery management system includescatastrophic fault protection to monitors the cells of the battery packfor over voltage or over current conditions. When a fault is sensed, asignal is provided that drives the gate of one or more n-FET devices toopen the main bus of the battery to interrupt current flow from thebattery.

In yet another aspect, the battery management system includes a gasgauge function that monitors the charging and discharging of the batterypack and then determines, based on stored information and currentinformation a value related to an estimated amount of charge availablefrom the battery pack.

In a further aspect, the battery management system of the presentinvention includes circuitry configured to boost the voltage provided todrive the gate of one or more n-FET devices to full on so as to allowfor the maximum flow of current through the n-FET devices.

In a still further aspect, the battery management system of the presentinvention may also include circuitry designed to isolate the terminalsof the battery pack unless the battery pack is inserted into a chargeror a device to be powered by the battery. Such isolation results in azero voltage across the battery terminals when the battery is notinserted into a charger or device to be powered, thus preventinginadvertent shorting of the terminals which could lead to catastrophicdischarge of the battery and possible harm to equipment or to a user.

In yet another further aspect, the battery management system of thepresent invention may include one or more processors for controlling thevarious functions of the battery management system. In another aspect,the one or more processors may be configured to communicate withinternal and/or external memory storage or devices to provide forstorage of events that occur during charging, discharging and storage ofthe battery pack. In still another aspect, the processors may beconfigured to communicate not only with internal or external storagemedia or devices, but may also be configured to communicate over anetwork with other processors, storage media or devices, or even otherbatteries or battery chargers. The network may be either wired orwireless.

In another aspect, the present invention includes a battery pack forpowering a device, comprising: a rechargeable cell having a positive anda negative terminal; a main bus connecting the positive terminal of therechargeable cell with a positive connector of a battery pack connectorand also connecting the negative terminal of the rechargeable cell witha negative connector of the battery pack connector; and a batterymanagement system in electrical communication with the rechargeablecell, including a processor for monitoring an input related to the stateof charge of the cell, a switch disposed in the front-side bus betweenthe positive terminal of the cell and the positive connector of thebattery pack, the switch responsive to a signal generated by theprocessor in response to the input related to the state of charge of thecell to control the charging or discharging of the cell.

In one alternative aspect, the switch is a n-FET device. Anotheralternative aspect further comprises a second rechargeable cellconnected in series with the first rechargeable cell; and a monitoringcircuit, in electrical communication with the processor, the monitoringcircuit monitoring the voltage of the first and second rechargeablecells and providing a signal for each rechargeable cell to theprocessor, the signal representative of a level of voltage measuredacross a negative and positive terminal of each cell, the monitoringcircuit including a first switch connecting the first rechargeable cellto a first bleeder circuit, the first switch responsive to anovervoltage signal from the processor to close the first switch toprevent overcharging of the first rechargeable cell, the monitoringcircuit also including a second switch connecting the secondrechargeable cell to a second bleeder circuit, the second switchresponsive to an overvoltage signal from the processor to close thesecond switch to prevent overcharging of the second rechargeable cell.

Still another aspect further comprises a temperature monitoring circuitfor monitoring the temperature of the battery pack and for providing asignal related to the temperature of the battery pack to the processor;and wherein the processor receives and analyses the temperature signalto determine if the temperature of the battery pack is within apre-selected range of temperature, and if the temperature of the batterypack is not within the pre-selected range of temperatures, the processorprovides a signal to the switch to disconnect the positive terminal ofthe cell from the positive connector of the battery pack.

Yet another aspect further comprises a state of charge monitoringcircuit for providing an indication of the amount of charge availablefrom the battery pack for powering a device. Still another aspectfurther comprises a battery pack isolation circuit in electricalcommunication with the processor, the battery isolation circuitconfigured to provide a connection signal to the processor indicatingthat the connector of the battery pack are connected to a batterycharger or device to be powered; and wherein the processor responds tothe connection signal by sending a signal to the switch to close theswitch to provide a voltage across the positive and negative terminalsof the connector.

In yet another aspect, the battery pack isolation circuit includes amechanical switch that has a closed condition when the battery connectorof the battery pack is connected to a battery charger or device to bepowered; and wherein the processor responds to the closed condition ofthe mechanical switch to provide a voltage across the positive andnegative terminals of the connector.

Still another aspect includes a communication bus connecting theprocessor to the connector and to other components of the batterymanagement system, the communication bus configured to providecommunication between the processor and the other components of thebattery management system, and to other systems, processors, networks orstorage media external to the battery pack.

Yet another aspect includes indicator means mounted on an exterior ofthe battery pack, the indicator means providing a visual indication ofinformation related to the operation of the battery. In one alternativeaspect, the indicator means is at least one light emitting diode.

In still another aspect, the present invention includes an intelligentbattery pack, comprising: a housing; a connector mounted on an end ofthe housing and configured to engage a connector disposed in or on adevice to be powered; a plurality of rechargeable battery cells, each ofthe cells having a positive and a negative terminal, and each of thecells connected in series by a main bus having a positive side connectedto a positive terminal of the connector and a negative side connected toa negative terminal of the connector, the plurality of cells disposedwithin the housing; a switch disposed in the positive side of the mainbus between the positive terminal of the connector and the plurality ofcells; a processor for controlling the operation of the battery pack; aprimary protection circuit in electrical communication with theprocessor, the primary protection circuit including: a plurality ofmonitoring circuits in electrical communication, each one of theplurality of monitoring circuits for monitoring a parameter related tothe state of charge of an individual one of the plurality of cells, anda plurality of bleed circuits, each of the plurality of bleed circuitsconnected to an individual one of the cells to bleed the cells inresponse to the parameter for the cell monitored by the monitoringcircuit connected to that cell to prevent an overcharge of the cell; asecondary protection circuit for protection of battery pack from shortcircuits; a battery management system in electrical communication withthe connector, the switch and the plurality of monitoring circuits, thebattery management system configured to monitor the charging anddischarging of the cells and to provide a signal to the switch to openthe switch if a fault is detected; a state of charge monitoring circuit,including a sensor for determining an amount of current flowing throughthe main bus, a state of charge processor in electrical communicationwith the sensor, a state of charge memory in electrical communicationwith the state of charge processor, the memory for storing informationrelated to the battery cells and also to the amount of current flowingthrough the main bus, wherein the state of charge processor, based onthe information stored in the state of charge memory and input from thesensor determines the amount of current available from the battery; anda communication bus in electrical communication with the connector, theprocessor, the primary protection circuit, the secondary protectioncircuit, the battery management system and the state of chargemonitoring system for providing for communications between theconnector, the processor, the primary protection circuit, the secondaryprotection circuit, the battery management system and the state ofcharge monitoring system.

In an alternative aspect, the switch is an n-channel field effecttransistor. In still another alternative aspect, the primary protectioncircuit includes a primary protection processor configured to monitorthe charging and discharging of the cells. In a further alternativeaspect, the primary protection circuit includes a primary protectionprocessor configured to control the charging and discharging of thecells.

In yet another aspect, the processor is also configured to communicateinformation through the communication bus to the state of chargeprocessor, the information used by the state of charge processor todetermine the amount of current available from the battery cells and tostore the determined amount of current available in the state of chargememory.

Still another aspect includes a temperature monitoring circuit todetermine the temperature of the battery back, the temperaturemonitoring circuit communicating the temperature of the battery pack tothe primary protection circuit; and wherein the primary protectioncircuit is configured to send a signal to the switch to open the switchif the temperature of the battery pack is not within a pre-selectedrange of temperature values.

In yet another aspect, the intelligent battery pack further comprises abattery pack isolation circuit in electrical communication with theprocessor, the battery isolation circuit configured to provide aconnection signal to the processor indicating that the connector of thebattery pack is connected to a battery charger or device to be powered;and wherein the processor responds to the connection signal by sending asignal to the switch to close the switch to provide a voltage across thepositive and negative terminals of the connector.

In another alternative aspect, the present invention includes a deviceto be powered by either the battery pack or the intelligent battery packdescribed above. In one alternative aspect, the device is a medicaldevice. In another alternative aspect, the device is a mechanicalcompression device. In a further aspect, the battery pack or intelligentbattery pack is configured to power a mechanical compression device forat least thirty minutes. In still another aspect, the battery pack orintelligent battery pack is configured to power a mechanical compressiondevice for at least 20 minutes when the mechanical compression device isused to treat a larger than average size patient. In yet another aspect,the battery pack or intelligent battery pack

Other features and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of performing chest compressions on apatient by using a mechanical chest compression device.

FIG. 2 is perspective view of the mechanical chest compression device ofFIG. 1 showing the bottom and front sides of the device

FIG. 3 is a perspective view of the mechanical chest compression deviceof FIG. 1 showing the bottom and rear cover plates removed.

FIG. 4A is perspective view of a battery pack in accordance with thepresent invention showing a battery latch disposed on a front side ofthe battery pack.

FIG. 4B is a perspective view of the battery pack of FIG. 4A showing aconnector, indicator and button disposed on a back side of the batterypack.

FIG. 5 is an exploded perspective view illustrating various componentsof one embodiment of a battery pack of the present invention.

FIG. 6 is a schematic diagram of an embodiment of battery managementsystem in accordance with principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The various embodiments of the present invention are directed toproviding a rechargeable battery for powering mobile equipment,particularly medical devices. The embodiments of the invention areparticularly advantageous when the battery is required to provide alarge amount of current over a predictable period of time. Moreover, theembodiments of the invention include a battery management system thatcontrols all aspects of the operation of the battery, and also includesa memory in which events related to the battery that occur during thebattery's lifetime are stored. Moreover, embodiments of the batterymanagement system include the capability of accommodating batteriesusing different battery chemistries, and are also capable of beingupdated through a communication port.

While the various embodiments of the invention are described withreference to a mechanical compressions device, those skilled in the artwill immediately appreciate that those embodiments are not to be limitedto powering such a device. Indeed, such a use is merely exemplary, and abattery in accordance with the various embodiments of the presentinvention may be used to power any device, and in particular, medicaldevices, wherein the design requirements of the device are met by thecapabilities of such a battery.

When a battery in accordance with the various embodiments of the presentinvention is used with a mechanical compression device, the battery mustbe capable of powering the mechanical compression device for long enoughto treat the patient not only in the field, but also during transport ofthe patient from the field to a care center. Experience has shown,however, that a patient's size and weight are factors that determine theamount of current drain on the battery during treatment. Accordingly,treatment of a larger than average patient results in a larger currentdraw on the battery.

For example, studies have found that the chest depth, chest breadth andchest circumference are factors influencing the amount of current drainon a battery powering a mechanical compression device. Other studieshave observed that the mean chest depth of an average adult human maleis 9.4 inches, mean chest breadth is 12.2 inches and mean chestcircumference is 39.7 inches. See, Young, J W, R F Chandler, C C Snow, KM Robinette, G F Zehner, M S Lofberg, Anthropometric and MassDistribution Characteristics of the Adult Female, FAA Civil AeromedicalInstitute, Oklahoma City, Okla., Report No. FAA-AM-83-16, 1983;Anthropometry and Mass Distribution for Human Analogues: Volume 1:Military Male Aviators, Report No. USAFSAM-TR-88-6, March, 1988;Haslegrave, C M, “Characterizing the anthropometric extremes of thepopulation”, Ergonomics, 29:2, pp. 281-301, 1986; Diffrient, N, A RTilley, J C Bardagy, Human Scale 1/2/3, The MIT Press, Cambridge, Mass.,1974; and PeopleSize Pro Software, Open Ergonomics Ltd., 34 BakewellRoad, Loughborough, Leicestershire, LE11 5QY, United Kingdom, theentireties of which are hereby incorporated by reference herein. Abattery that can sustain operation of the mechanical compression devicefor at least thirty minutes for an average size patient, and at leasttwenty minutes for a larger than average size patient is advantageous.

Referring now to the drawings in detail, in which like referencenumerals indicate like or corresponding elements among the severalfigures, there is shown in FIG. 1 a chest compression belt fitted on apatient 1. A chest compression device 2 applies compressions with thebelt 3, which has a right belt portion 3R and a left belt portion 3L.The chest compression device 2 includes a belt drive platform 4 and acompression belt cartridge 5 (which includes the belt). The belt driveplatform includes a housing 6 upon which the patient rests, a means fortightening the belt, a processor and a user interface disposed on thehousing. The belt includes pull straps 18 and 19 and wide loaddistribution sections 16 and 17 at the ends of the belt. The means fortightening the belt includes a motor attached to a drive spool, aroundwhich the belt spools and tightens during use. The design of the chestcompression device, as shown herein, allows for a lightweightelectro-mechanical chest compression device. The fully assembled chestcompression device weighs only 29 pounds, and is thus hand-portable overlong distances. The device itself weighs about 22.0 to 23.0 pounds, withthe battery, in at least one embodiment of the present invention,weighing between 2 and 5.0 pounds, and preferably about 3 pounds. Thebelt cartridge weighs about 0.8 pounds and the straps to secure thepatient weigh about 1.6 pounds.

FIG. 2 shows the posterior side 23 of the chest compression device asseen from the superior direction. In the perspective of FIG. 2, theaverage sized patient's buttocks and the back of the patient's legswould extend past the inferior bumper 40. The device is built around asturdy channel beam 41 that is laterally oriented with respect to thehousing. The channel beam supports the device against the forces createdduring compressions. The channel beam also serves as the structure towhich the belt cartridge is attached.

The channel beam 41 forms a channel extending across the lateral widthof the device. During compressions, the belt is disposed in and travelsalong the channel. The belt is attached to a drive spool 42 that spansthe channel.

FIG. 3 shows internal components of the chest compression device 2. Amotor 79 is operable to provide torque to the drive spool 42 through aclutch 80 and a gearbox 81. A brake 82, attached to the superior side ofthe motor, is operable to brake the motion of the drive spool. The brakehub connects directly to the rotor shaft of the motor.

The motor 79 and brake 82 are controlled by a processor unit 83, motorcontroller 84 and power distribution controller, all of which aremounted to the inside of the anterior cover plate 60. The processor unitincludes a computer processor, a non-volatile memory device and adisplay.

The processor unit is provided with software used to control the powercontroller and the motor controller. Together, the processor unit, powercontroller and motor controller make up a control system capable ofprecisely controlling the operation of the motor. Thus, the timing andforce of compressions are automatically and precisely controlled forpatients of varying sizes.

FIGS. 2 and 3 also show the location of a battery compartment 121 nearthe head of the patient. The location and design of the battery pack andbattery compartment allow for rapid exchange of batteries. A spring inthe back of the compartment forces the battery pack out unless thebattery pack is fully and correctly inserted in the compartment. A latchon one end of the battery pack engages a receiver in the batterycompartment 121 to hold the battery pack within the batter compartmentwhen the battery pack is inserted into the battery compartment. Recesses120 indicate the location of the springs inside the battery compartment121. Plastic grills 122 at the end of the battery compartment reinforcethe recesses.

FIGS. 4A and 4B are perspective views of a battery pack 200 showing thefront and back sides 205, 210 of the battery pack respectively. Frontside 205 of the battery pack faces outward and is visible to the userwhen the battery pack is inserted into the battery compartment 121 (FIG.3). As shown in FIG. 4A, front side 205 includes a latch 215 thatengages a receiver within battery compartment 121 to hold the batterypack 200 within the battery compartment. Also shown in FIG. 4A are apair of raised tabs 217 disposed on the tops side of the front end ofthe battery pack. These tabs cooperate with the latch to ensure that thebattery is properly seated in the battery compartment by prevent the topof the battery from riding up during battery insertion, forcing thelatch into proper engagement with a battery latch receiver or lip of thebattery compartment.

The back side 210 of the battery pack, as seen in FIG. 4B, includes aconnection 220 that connects to a connector within battery compartment121 to enable electrical communication between the controller orprocessor of the mechanical compression device and the battery pack 200.This connector not only allows for the flow of current from the batterypack to power the mechanical compression device, but it also providesfor the flow of data, programming commands and other information, suchas battery charge status, discharge rate, time remaining untildischarged, and the like between the battery pack and the processor orcomputer controlling the operation of the mechanical compression device.Similarly, connector 220 may be configured to be connected to aconnector in a battery charger to charge the cells of the battery pack,as well as to provide for the flow of data, software programs orcommands and/or other information between the charger and the batterypack. It is also contemplated that connector 220 may be used to connectthe battery pack to a communication network that would allow for flow ofinformation between the battery pack and other computers, servers,processor or devices that are also connected to the network. It will beunderstood that the network may be a wired network, such as, forexample, an Ethernet, or it may be a wireless network. The network maybe a local network, or it may be a wide area network, such as a WLAN orthe Internet.

A status indicator 225, which may be, for example, one or more lightemitting diodes (LEDs) or similar devices, is also disposed on the backend 210 of battery pack 200 to provide a visual indication of, forexample, the charge/discharge status of the battery pack, the presenceof any faults that would affect the operation of the battery pack, orother information that might be useful to the user of the battery. Apush button 230 is also included; button 230 may be used, for example,to initiate a reset of the battery pack. Alternatively, button 230 maybe used to initiate a diagnostic test, the results of which may beindicated by status indicator 225. In other embodiments, pressing button230 may initiate other functions of the processor in the battery pack,including, for example, and not by way of limitation, determining theremaining capacity of the battery, display of fault codes through theuse of status indicator 225 and the like.

FIG. 5 is an exploded perspective view of the battery pack 200. Thebattery pack 200 in this exploded view has been inverted from the viewof FIGS. 4A and 4B. The battery pack has a bottom enclosure 234 and atop enclosure 232. A battery latch assembly having a battery latch 236,a lever base 238 and a lever latch 240 is mounted at the side of thebattery pack facing outward when the battery pack is inserted into abattery compartment, and is held in place by the bottom and topenclosures. Lever latch 240 has a wing 241 that is inserted into agroove or slot 243 formed in a face of battery latch 236, and lever base238 is mounted on the bottom enclosure to pivotally hold lever latch 240in the enclosure. Compression springs 254 are disposed between a bottomend of battery latch 236 and top enclosure 232. A projection 255 isdisposed a top end of battery latch 238, and is configured to protrudethrough slot 251 that extends through a thickness of the bottomenclosure 234. In this manner, battery latch 236 may be manipulated by auser to engage and disengage projection 255 from the latch receiverlocated in the mechanical compression device to insert the battery packinto the battery compartment and to release the battery pack for removalfrom battery compartment 121.

Disposed at the back end 210 of the battery pack is a battery entryboard 242 to which is mounted connector 220, indicator 225 and button230 (FIG. 4B). Entry board 256 is mounted to bottom enclosure 232 usingone or more screws 250. The entry board may also be fastened to topenclosure 252 using one or more screws 256. In some embodiments, a waterresistant gasket 262 may be used to resist the incursion of fluids intothe interior of the battery pack. Moreover, a label 260 may be used toprovide information to a user relative to the various indications thatmay be provided by indicator(s) 225.

A battery management board 244 to which is mounted processors, memoryand electrical circuitry for managing the various operations of thebattery (which is described in more detail below) is mounted usingscrews or other fasteners 258 to battery cell assembly 246. Battery cellassembly 246 includes one or more battery cells 248. Battery cells 248may be cells utilizing a variety of battery chemistries, such as, forexample, nickel metal hydride, lithium hydride, lithium-ion and thelike. Battery management board 244 and battery cell assembly 246 mayalso include a pair of splatter shields 266 mounted on left and rightsides of battery cell assembly 246 to protect the terminals of theindividual battery cells 248 from inadvertent contact with other partsof the assembly, thus providing a shield against short circuit of thebattery cells.

Battery pack 200 also includes at least one vent 264, shown disposed inthe top enclosure to allow for venting of the battery pack to preventbuildup of potentially flammable or explosive gases produced by thebattery cells 248 during charging or discharging of the battery pack.While shown disposed in the top enclosure, those skilled in the art willappreciate that the vents may be disposed through any wall or side ofthe battery pack. Vents 264 may be a simple hole extending through thewall or side of the battery pack. Alternatively, vent 264 may include afiltering means 265, such as a screen or hydrophobic membrane to preventthe incursion of particulates or fluids or moisture into the interior ofthe battery pack. An additional advantage of such vents is that the ventor vents provide for equalization of pressure between the interior andexterior of the battery pack, such as may occur when the battery pack istransported to a higher or lower altitude.

The mechanical compression device described above requires a reliablepower source to operate. It is not unusual for the device to be requiredto be used for thirty minutes or more to provide resuscitation to apatient in an emergency. The torque and power requirements of the motorof the mechanical compression device require up to a peak of seventyamperes of current during compression. If enough current cannot bedelivered by the battery to the motor controlling the compressions, thevoltage falls off and the motor may not be capable of generating enoughtorque to ensure complete compression of a patient's chest.

The inventors of the present invention have realized that having a verylow total internal resistance is key to ensuring extended and reliableoperation of the battery when the battery is under a constant powerdrain. One such battery chemistry that has been found to be useful indevices requiring high power is a battery using Lithium Ion chemistry,such as the model ANR26650M1-A or ANR26650M1-B Lithium Ion cellavailable from A123 Systems, Incorporated.

FIG. 6 is a schematic diagram illustrating one embodiment of a batterypack 300 in accordance with the present invention. Battery pack 300includes eleven Li-Ion chemistry cells, such as the model ANR26650M1-Aor ANR26650M1-B cells described above. Each cell provides 3.3 volts, andthe eleven cells are connected in series to provide a total of 36.3volts. Using such cells, one embodiment of a battery pack in accordancewith principles of the present invention can be manufactured that weighsapproximately three pounds. Such a battery has been observed to deliverbetween 1550 and 2000 watts, and preferably deliver a peak power of 1800watts. This provides a desirable weight to power ratio. Moreover, suchan embodiment has also been found to be able to deliver energy ofslightly less than 100 watt/hours. While eleven battery cells are usedin this exemplary embodiment, more or less cells could be used dependingon the requirements of the device to be powered.

To provide the amount of current required to operate the motor of thecompression device, the inventors have discovered that it is importantto minimize the internal resistance of the battery pack. Accordingly,the Lithium Ion (Li-Ion) cells used should have low internal DCresistance, preferably below 15 milliohms, and more preferably below12.5 milliohms per cell.

While Li-Ion batteries are capable of providing the voltage and currentrequired to operate a mechanical compression device for extended periodsof time, care must be taken during both the discharge phase, andrecharge of the batteries to ensure that the batteries continue tofunction for their desired lifetimes. It is well known that Li-Ion cellsshould not be over charged, nor should they be over discharged.Accordingly, various embodiments of the present invention include thecapability of monitoring and controlling both the discharge of the cellsand the recharging cycle. Those embodiments will be discussed in moredetail below.

As described previously, the eleven Li-Ion cells 310 are connected inseries by a main power bus 320. Bus 320 has both a positive side and anegative, or ground side, as is typical for a DC circuit. Bus 320delivers the direct current provided by the battery cells to a load (inthis example, the mechanical compression device) through an interface330. As shown in FIG. 6, interface 330 is a pin connector having sevenconnection pins. Alternatively, a socket could be used, or a combinationof pins and sockets, with more or less than seven pins or sockets couldbe used.

The positive side of bus 320 is connected to pin 7 of interface 330.Similarly, the negative side of bus 320 is connected to pin 6 ofinterface 330. Pins 1-5 of interface are used to communicate varioussignals involved in the monitoring and control of the battery pack, aswell as for communication to the device that is being powered, enablingthe exchange of information and control signals between the battery packand the powered device. Various exemplary embodiments of the inventionincorporating those features will be discussed in more detail below.

Returning again to FIG. 6, the positive side of bus 320 includes a fuse342 to protect the circuit from over current conditions. Fuse 342 maybe, for example, a 30 ampere fuse. In such a case, a sustained currentflow through fuse 342 of more than 30 amperes would cause the fuse toopen, breaking the circuit created by bus 320 and stopping the flow ofcurrent from the battery cells. While not shown, there is also a blownfuse detector circuit that monitors the fuse, and, if the fuse is blown,provides a signal to the pack controller that the fuse is blown. Thepack controller may then provide a signal indicating that the battery isnot suitable for use. Such a signal, for example, may be the change incolor of and LED, or activation or de-activation of some other statusindicator. Alternatively, the pack control may provide a signal to theequipment powered by the battery, which may then provide an indicationto a user that the battery is not ready for use.

The positive side of main bus 320 also includes a number of n-channelfield effect transistors (n-FET) 340, 350 and 360. These n-FETs providefor switching and control of the circuit. N-FETs are used because theyprovide a very low resistance switch in keeping with the designrequirement of minimizing the total internal resistance of the battery.Another unique capability of the n-FET is that they are capable ofconducting high current loads, without damage and without generatingexcessive amounts of heat. One example of an n-FET that has been foundsuitable for use in various embodiments of the present invention is themodel IRLS3036, available from Digi-Key Corporation.

In typical designs, p-FET devices would be used as the switches andwould be placed in the high side of the main bus. However, p-FETS havetwo or more times the on resistance of an n-FET device. Thus, to handlethe same current as an n-FET device, several p-FETs wired in parallelwould be needed. Moreover, use of several p-FETS may also require theuse of a heat sink to dissipate heat generated while the p-FET is on.This is disadvantageous where space within the battery pack is limited.

Similarly, an n-FET device would typically be used in the low side ofthe main bus to switch the current on and off in the bus. However, useof an n-FET in this situation breaks the ground of the battery, whichmay cause noise in the circuit and interfere with communication betweenthe various elements of the battery management system circuitry.Accordingly, the inventions have placed the n-FET switches in the highside of the bus, which provides efficient switching of the bus withoutthe generation of excess heat that may occur when p-FETs are used.Placing the n-FETs in the high side of the bus also eliminates theproblem of breaking the ground of circuit.

In some embodiments, one or more resistors, such as resistors 370 and380, may be inserted in the negative, or low, side of the main buscircuit. These resistors provide the ability to tap the main bus tomonitor various aspects of the current flowing through the circuit. Forexample, in one embodiment, resistor 370 is connected across the inputlines of a cell balancing and primary protection circuit, which isdiscussed in more detail below. A typical value for resistor 370 is, forexample, 2.5 milliohms.

In another embodiment, resistor 380 may be connected across astate-of-charge monitor, also known as a “gas gauge.” In thisembodiment, the value of resistor 380 may be, for example, 5 milliohms.

Each of the cells 310 is individually monitored during both charging anddischarging to control the rate of charging and discharging,respectively. In one exemplary embodiment, as shown in FIG. 6, aseparate cell tap line 390 is connected to each cell and to a cellmonitoring and balancing circuit 400.

Primary Protection

During charging, the voltage of each cell is independently monitored toprevent overcharging of the cell. In one exemplary embodiment, amonitoring system on a microchip, which may be, for example, batterypack protection and monitor integrated circuit (IC) 410 such as an OZ890available from O₂ Micro, is used to control the charging of the variouscells. In such an arrangement, cell monitoring line 390 provides apositive signal to a representative pin input of IC 410. For example,cell 1 is monitored using input line BC1 of IC 410, and so forth up tocell 11, which is monitored using input line BC11 of IC 410.

If the control circuitry of IC 410 detects an imbalance in a cell, IC410 provides a signal on an appropriate external bleed control lineCB1-CB11. As shown in FIG. 6, when the signal on the appropriateexternal bleed control line is applied to the gate of n-FET 420, currentis allowed to pass between the source and the drain of n-FET 420 andthen through resistor 430, which results in bypassing the cell andhalting charging of the cell. As can be seen from FIG. 6, each cell hasits own dedicated combination of resistor and n-FET in electricalcommunication with IC 410 for monitoring each cell and preventing eachindividual cell from over charging.

Cell balancing and primary protection IC 410 may also be used in someembodiments to monitor the total voltage of the battery cell pack. Forexample, when all of the cells have attained their maximum voltage, IC410 can send a low signal to the gate of n-FET 350 to open the channelbetween the source an drain of n-FET 350 and thus open the main buscircuit 320. This results in a cessation of charging current through thecells, and thus halts the charging process.

Similarly, IC 410 monitors the voltage across the cells during dischargeof the battery. When the voltage across the cells drops below athreshold level, for example, 21 volts, IC 410 drives the signal on line450 low, which in turn shuts off n-FET 360 which interrupts the main buscircuit. This prevents damage to the battery cells that may be caused byremoving too much of the charge in the cells, which may result indecreased life of the cell.

IC 410 may also include and control a temperature measurement capabilitydesigned to monitor the temperature of the battery pack and/orindividual battery cells to prevent overheating. In this embodiment, oneor more thermistors 460 are used to provide temperature signals overline 470 to the IC 410. If IC 410 determines that the temperature of thebattery is either too high or too low, IC 410 may drive either or bothof n-FETs 350 and 360 low, opening the main bus 320 and isolating thebattery pack. It will be understood that while only a single line 470 isshown for clarity, line 470 includes an appropriate number of conductorsto monitor the function of all thermistors used in the temperaturemonitoring circuit in communication with IC 410.

IC 410 may additionally provide a visual indication of fault state byproviding a fault signal on line 480 that may then be used to cause LED490 to light up. This visual signal of a fault condition sensed by theprimary protection circuit indicates that the battery pack has beenrendered non-functional by IC 410 and that repair or maintenance of thebattery pack may be required.

Secondary Protection

Some embodiments of the present invention may also include secondaryprotection against catastrophic faults or over voltage protection. Suchsecondary protection may be provided by a variety of circuits designedto monitor the voltage of the battery pack and/or the current flowthrough the main bus and to take action when certain thresholds valuesof current or voltage are exceeded. In one embodiment, such protectionmay be provided by an integrated circuit 500, such as, for example, theOZ8800 available from O₂Micro. Those skilled in the art will know that,depending on the number of cells used in the battery pack, more than oneIC 500 may be required. For example, the OZ8800 secondary level batteryprotection integrated circuit can monitor three to seven individualcells. Thus, where eleven cells are used, two OZ8800s will be required.

IC 500 monitors the voltage of each cell over monitoring line 312. Insome embodiments, a time delay may be employed that provides fortemporary over voltage conditions to exist. Where the time threshold isexceeded because the voltage did not drop back into an acceptable range,IC 500 sends a low signal over fault line 510 to n-FET 340 to turn offn-FET 340. Each cell is monitored by a similar circuit.

It should be apparent from FIG. 6 that the n-FETs described above are ina normally off state unless a positive voltage is applied to the gate ofeach n-FET. Thus, any fault that results in voltage decrease to a levelbelow the threshold of the n-FET at the gate will cause the n-FET toopen, thus providing additional protection to the cells and batterymanagement circuitry.

Gas Gauge

Another embodiment of the present invention includes a “gas gauge”function that monitors the amount of useful charge remaining in thebattery pack. Such gas gauge functionality can be provided usingintegrated circuits designed to carry out vary tasks, such as tocalculate remaining battery capacity for use and standby conditionsbased on time of use, rate of discharge and the temperature of thebattery. Such a circuit may also determine the true battery capacity inthe course of a discharge cycle from near full charge to near fulldischarge states.

FIG. 6 illustrates one example of such a gas gauge circuit 600.Monitoring of the battery pack is accomplished using an integratedcircuit 610, such as a bq2060A available from Texas Instruments, Inc. IC610 works in conjunction with an external EEPROM 620. EEPROM 620 storesconfiguration information for IC 610, such as the chemistry used in thebattery cells, the self-discharge rate of the battery, various ratecompensation factors, measurement calibration, and battery designvoltage and capacity. All of these settings can be changed to allow thesystem to be used with a variety of battery types. Moreover, IC 610 cancommunicate with a central processor and memory over a back-side buscircuit 630. In this manner, IC 610 and EEPROM 620 may be configured,using control signals from the central processor, to accommodatedifferent types of batteries that are detected and identified by othercircuitry included in the system, or which are manually identified by auser. In an alternative embodiment, IC 610 may also cooperate with thepack controller to augment the reporting accuracy of the gas gauge ininstances of low current draw using appropriate control commandsembedded into the software that controls the operation of the packcontroller and the gas gauge to implement the algorithms necessary tocarry out this function.

In general, the gas gauge functions are carried out by IC 610 inconjunction with IC 800 to determines full charge battery capacity andthe capacity remaining at any point in time by monitoring the amount ofcharge input or removed from the battery cells. In addition, IC 610measures battery voltage, battery temperature and current as detectedacross resistor 380. IC 610 also, in some embodiments, may estimate theself-discharge rate of the battery, and also monitors for low-voltagethresholds of the battery. As described, IC 610 measures the amount ofcharge and discharge of the battery by monitoring the voltage acrossresistor 380, which is located between the negative terminal of thefirst cell 310 (of the series connected cells) the negative terminal ofthe battery pack. Available battery charge is determined from thismeasured voltage and correcting the measurement for environmental andoperating conditions.

IC 610 may also measure the temperature of the battery pack so as tocarry out the estimations and adjustments described above. In oneembodiment, a thermistor 640 is mounted adjacent to a cell or cells ofthe battery pack in such a manner as to be able to measure thetemperature of the cell or cells of the battery pack. IC 610 drives thegate of n-FET 650 high by providing an appropriate signal over line 660to connect a bias voltage source to thermistor 640 while the temperatureof the cell or cells is being measured. Once the measurement iscompleted, IC 610 drives the gate of n-FET 650 low, opening the n-FETand thus disconnecting thermistor 640 from the bias source.

IC 610 may be reset each time the battery is charged so that thereported amount of charge remaining in the battery is accurate. Abattery pack supervisor circuit or pack controller 800, to be describedin more detail below, provides a signal over reset line 670 to drive thegate of n-FET 680 high. This causes the current to flow through n-FET680, resulting in a reset signal being provided to IC 610 to reset thebattery capacity counter of IC 610.

In another embodiment, IC 610 may include a seal/unseal function thatprevents unauthorized access to the parameters stored in the IC 610 orEEPROM 620. Pack controller 800 may send a signal over line 680 thatdrives the gate of n-FET 690 high, which closes n-FET 690 allowing forcommands and data to flow between IC 610 and EEPROM 630. Such data mayinclude, for example, updated calibration information and the like. Inan alternative embodiment, the flow of data between IC 610 and EEPROM630 may be controlled using only software commands from the packcontroller to control IC 610 and EEPROM 630 without requiring n-FET 690.

Pack Controller

In another embodiment of the present invention, the battery managementsystem includes a pack controller 800 which serves as an overallsupervisor for the various functions carried out by the batterymanagement system. Pack controller 800 will typically be an integratedcircuit, although discrete circuitry carrying out the same functionscould be used, depending on the amount of space available within theconfines of the battery pack.

For example, pack controller 800 may be a low or ultra-low powermicrocontroller such as the MSP430F2418 Mixed Signal Controlleravailable from Texas Instruments Incorporated. Such a controller mayinclude memory, such as random access memory or flash memory to providefor rapid and efficient execution of the various functions of thebattery management system. Pack controller 800 also has the capabilityof communicating with peripheral devices, circuitry or memory over oneor more communication buses, such as backside bus 630 and front-side810. The communication busses typically use a communication protocolsuch as, for example, the I²C bus (a Trademark of Philips Incorporated)or the System Management Bus (SMBus). The SMBus is described in moredetail below.

Appropriate software commands are used to program the functions of thepack controller 800. Such software includes commands configuring thecommunication protocol interface, such as for example, the SMBusinterface. The software would also configure the pack controller tomonitor critical battery pack parameters, which are made available to itover communication lines 810, 820, 822, back-side bus 630, front sidebus 810 and detect line 824, as well as other communications lines notshown or which may be added in the future.

When appropriately programmed, pack controller 800 is also incommunication with one or more memory devices, such as, for example, anevent archive EEPROM 900. Such an archive has, for example, although notlimited to, 64 kilobytes of memory that can be used to store history ofvarious events that occur during the charge and discharge cycles of thebattery pack, such as, for examples, the total amount of charge, totalamount of energy discharged, the temperature of the battery cells, anyfaults that occur, or other information related to the individualbattery cells and/or the various circuits employed to manage and controlthe operation of the battery.

Pack controller 800 may also be programmed to communicate with memoryand/or processors such as, for example, EEPROM 1000. In the exemplaryembodiment shown in FIG. 6, EEPROM 1000 may be located in a mechanicalcompression device that is powered by the battery pack, or it may beincorporated into the battery pack and configured to be accessed by thedevices to be powered by the battery. In this example, pack controller800 communicates with EEPROM 1000 and/or a processor in the mechanicalcompression device over front side bus 810, which accesses a similar busin the mechanical compression device through connector 330. In thismanner, a two-way communication connection may be established betweenthe battery pack and a device powered by the battery pack to allow forexchange of information between the battery pack and the powered device.For example, updated operating parameters or commands, including updatedsoftware, may be loaded into the battery pack from the powered devicewhen the battery pack is put into communication with the powered device.Similarly, information contained in the event archive EEPROM 900 may betransmitted to the EEPROM 1000, or any other memory (such as a portablememory device) configured for communication over back-side bus 810 fromany of the memories present in the battery pack.

It will be understood that this communication capability also allows thebattery to communicate with other devices besides devices which will bepowered by the battery. For example, typically, the battery pack will beremoved from a powered device to be recharged. When the battery pack isconnected to a battery charger, the battery charger may be used toretrieve information from the memory or memories of the battery pack,and/or transmit updated data, information, programming commands orsoftware to the battery through front-side bus 810. This communicationprocess will typically be managed using various handshaking andcommunication dialog as set forth in the communication protocol used toenable the communication, such as the SMBus protocol, exchanged betweena processor residing in the charger or other device and the packcontroller 800 of the battery pack. In some embodiments, the battery mayalso be trickle charged when the battery is inserted into the device tobe powered, where the device being powered is also connected to anexternal power supply.

Still other embodiments of the present invention may include acapability, managed by pack controller 800, of recognizing when thebattery pack is inserted into a battery charger or device to be powered,such as a mechanical compression device. For example, pack controller800 may be configured using appropriate software and/or hardwarecommands to provide a signal to IC 410 and IC 500 to provide a highsignal to the gates of n-FETs 340, 350 and 360 to close those switchesand thus provide full battery voltage at the positive and negative pinsof connector 330 only when detect circuit 1100 sends an appropriatesignal to pack controller 800 over line 824 indicating that the batterypack is properly mounted into a device to be powered.

In one embodiment, pack controller 800 monitors a line connected to amechanical switch or interlock that is forced closed when the battery isproperly inserted into a charger or a device to be powered. In anotherembodiment, pack controller 800 monitors a signal line connected to oneor more pins of the battery connector. When an appropriate signal isreceived over this signal line, pack controller 800 determines that thebattery is inserted into a charger or a device to be powered, andprovides a high signal to the gates of n-FETs 340, 350 and 360 asdescribed above. This embodiment is particularly advantageous in thatpack controller 800 may be programmed to respond only when a particularsignal is received, ensuring that the battery is inserted into aspecific type or make of a charger or device to be powered designed toaccommodate the battery before providing the high signal to the gates ofn-FETs 340, 350 and 360.

These embodiments are advantageous in that discharge of the battery inthe event of an accidental short circuit across the positive andnegative terminals of connector 330 is prevented. Given the amount ofenergy stored in the cells of the battery pack, such a discharge couldbe catastrophic. Thus, in this embodiment, there is no voltage betweenthe positive and negative terminals of connector 330 of the battery packunless the battery pack is properly mounted in a device configured toprovide the appropriate signal to the detect circuit 1100, thusproviding for safe handling, storage and transport of the battery backwhen the battery pack is not connected to either a charger or a deviceto be powered, such as the mechanical compression device describedabove.

Pack controller 800 may also be programmed to provide password access toallow for changing of settings and parameters stored in EEPROMs 900 and620, as well as to provide appropriate signals to drive LED 490 in theevent of a fault. Additional capabilities may also be included,configured using appropriate software and/or hardware commands, toprovide additional functions to the battery management system. Forexample, such functions may include driving a display that indicates thetotal amount of charge remaining in the battery and the like. A morecomplete description of the various capabilities that can beincorporated into pack controller 800, particularly when pack controller800 is an MSP430F2418 (or other members of this controller family) iscontained in a document entitled “MSP430F241x, MSP430F261x Mixed SignalMicrocontroller,” SLAS541F—June 2007—Revised December 2009 availablefrom Texas Instruments Incorporated, the entirety of which is herebyincorporated herein by reference.

Smart Bus Communications

As will be apparent, the various processors and integrated circuits andlogic systems incorporated into the various embodiments of the presentinvention are capable of functioning as a unified system due to theirability to communicate with one another over the front side bus 320 andthe back side bus 630. In some embodiments, the communications overthese buses are carried out using the System Management Bus (SMBus)specification. The SMBus is a two-wire interface through which varioussystem component chips, such as IC 410, IC 610, the secondary protectionsystem 500, event archive 900, EEPROM 1000 and pack controller 800,among other circuitry, can communicate with each other and with the restof the system. Further information related to the SMBus specification iscontained in “System Management Bus (SMBus) Specification Version 2.0,”SBS Implementers Forum, Aug. 3, 2000, the entirety of which is herebyincorporated herein by reference.

Boost Circuit

The inventors have observed that, in some embodiments of the invention,the voltage required to drive the n-FETs closed exceeds the voltage thatis available from the battery pack. For example, using an n-FET thatrequires a bias voltage of 10 volts, the n-FET requires a drive voltageof the bias voltage plus the battery voltage to drive the n-FETsufficiently to allow an appropriate voltage to pass through the n-FETto charge or discharge the battery. Accordingly, a voltage boost circuitis included to boost the voltage supplied to the gates of the n-FETs todrive the n-FETs to conduct the current supplied by the battery cells.

Those skilled in the art will understand that the use of n-FETs in thepresent invention results in the need for complex circuitry, such as theboost circuit. Such complexity could be eliminated using p-FETs. Use ofp-FETs however, has been found to be disadvantageous because severalp-FETs may be needed to handle the same current that can be handled by asingle n-FET. Additionally, the heat generated using multiple p-FETs mayrequire the addition of one or more heat sinks to dissipate the heat,which may require more space in a compact battery than which isavailable. Moreover, it is well known that p-FETs have at least twicethe on resistance of n-FETs, which would increase the overall internalresistance of the battery pack.

While several particular foams of the invention have been illustratedand described, it will be apparent that various modifications can bemade without departing from the spirit and scope of the invention.

1-27. (canceled)
 28. A battery pack for powering a device, comprising: arechargeable cell having a positive and a negative terminal; a batterypack connector for connecting the battery pack to a charger or a deviceto be powered by the battery pack; a main bus connecting the positiveterminal of the rechargeable cell with a positive connector of thebattery pack connector and also connecting the negative terminal of therechargeable cell with a negative connector of the battery packconnector; and a battery management system in electrical communicationwith the rechargeable cell, including: a processor for monitoring aninput related to the state of charge of the cell, a switch disposed inthe front-side bus between the positive terminal of the cell and thepositive connector of the battery pack, the switch responsive to asignal generated by the processor in response to the input related tothe state of charge of the cell to control the charging or dischargingof the cell; a second rechargeable cell connected in series with thefirst rechargeable cell; a monitoring circuit, in electricalcommunication with the processor, the monitoring circuit monitoring thevoltage of the first and second rechargeable cells and providing asignal for each rechargeable cell to the processor, the signalrepresentative of a level of voltage measured across a negative andpositive terminal of each cell, the monitoring circuit including a firstswitch connecting the first rechargeable cell to a first bleedercircuit, the first switch responsive to an overvoltage signal from theprocessor to close the first switch to prevent overcharging of the firstrechargeable cell, the monitoring circuit also including a second switchconnecting the second rechargeable cell to a second bleeder circuit, thesecond switch responsive to an overvoltage signal from the processor toclose the second switch to prevent overcharging of the secondrechargeable cell; and a state of charge monitoring circuit, including asensor for determining an amount of current flowing through the mainbus, a state of charge processor in electrical communication with thesensor, a state of charge memory in electrical communication with thestate of charge processor, the memory for storing information related tothe battery cells and also to the amount of current flowing through themain bus, wherein the state of charge processor, based on theinformation stored in the state of charge memory and input from thesensor determines the amount of current available from the battery. 29.The battery pack of claim 28, wherein the switch is a n-FET.
 30. Thebattery pack of claim 29, further comprising a boost circuit inelectrical communication with the n-FET, the boost circuit configured toprovide a pre-determined bias voltage to a gate of the n-FET to drivethe n-FET to conduct a charging current to the first and secondrechargeable cells.
 31. The battery pack of claim 28, furthercomprising: a temperature monitoring circuit for monitoring thetemperature of the battery pack and for providing a signal related tothe temperature of the battery pack to the processor; and wherein theprocessor receives and analyses the temperature signal to determine ifthe temperature of the battery pack is within a pre-selected range oftemperature, and if the temperature of the battery pack is not withinthe pre-selected range of temperatures, the processor provides a signalto the switch to disconnect the positive terminal of the cell from thepositive connector of the battery pack.
 32. The battery pack of claim28, further comprising: a battery pack isolation circuit in electricalcommunication with the processor, the battery isolation circuitconfigured to provide a connection signal to the processor indicatingthat the connector of the battery pack are connected to a batterycharger or device to be powered; and wherein the processor responds tothe connection signal by sending a signal to the switch to close theswitch to provide a voltage across the positive and negative terminalsof the
 33. The battery pack of claim 28, further comprising: acommunication bus connecting the processor to the connector and to othercomponents of the battery management system, the communication busconfigured to provide communication between the processor and the othercomponents of the battery management system, and to other systems,processors, networks or storage media external to the battery pack. 34.The battery pack of claim 28, further comprising: an indicator mountedon an exterior of the battery pack, the indicator providing a visualindication of information related to the operation of the battery. 35.The battery pack of claim 34, wherein the indicator is an LED light. 36.An intelligent battery pack, comprising: a connector to engage aconnector disposed in or on a device to be powered; a plurality ofrechargeable battery cells, each of the cells having a positive and anegative terminal, and each of the cells connected in series by a mainbus having a positive side connected to a positive terminal of theconnector and a negative side connected to a negative terminal of theconnector; an n-FET disposed in the positive side of the main busbetween the positive terminal of the connector and the plurality ofcells; a processor for controlling the operation of the battery pack; aprimary protection circuit in electrical communication with theprocessor, the primary protection circuit including: a plurality ofmonitoring circuits in electrical communication, each one of theplurality of monitoring circuits for monitoring a parameter related tothe state of charge of an individual one of the plurality of cells, anda plurality of bleed circuits, each of the plurality of bleed circuitsconnected to an individual one of the cells to bleed the cells inresponse to the parameter for the cell monitored by the monitoringcircuit connected to that cell to prevent an overcharge of the cell; asecondary protection circuit for protection of battery pack from shortcircuits; a battery management system in electrical communication withthe connector, the n-FET and the plurality of monitoring circuits, thebattery management system configured to monitor the charging anddischarging of the cells and to provide a signal to the n-FET to openthe n-FET if a fault is detected; a state of charge monitoring circuit,including a sensor for determining an amount of current flowing throughthe main bus, a state of charge processor in electrical communicationwith the sensor, a state of charge memory in electrical communicationwith the state of charge processor, the memory for storing informationrelated to the battery cells and also to the amount of current flowingthrough the main bus, wherein the state of charge processor, based onthe information stored in the state of charge memory and input from thesensor determines the amount of current available from the battery; acommunication bus in electrical communication with the connector, theprocessor, the primary protection circuit, the secondary protectioncircuit, the battery management system and the state of chargemonitoring system for providing for communications between theconnector, the processor, the primary protection circuit, the secondaryprotection circuit, the battery management system and the state ofcharge monitoring system; and a boost circuit in electricalcommunication with the n-FET, the boost circuit configured to provide apre-determined bias voltage to a gate of the n-FET to drive the n-FET toconduct a charging current to the first and second rechargeable cells.37. The intelligent battery pack of claim 36, wherein the primaryprotection circuit includes a primary protection processor configured tomonitor the charging and discharging of the cells.
 38. The intelligentbattery pack of claim 36, wherein the primary protection circuitincludes a primary protection processor configured to control thecharging and discharging of the cells.
 39. The intelligent battery packof claim 36, further comprising: a temperature monitoring circuit todetermine the temperature of the battery back, the temperaturemonitoring circuit communicating the temperature of the battery pack tothe primary protection circuit; and wherein the primary protectioncircuit is configured to send a signal to the switch to open the switchif the temperature of the battery pack is not within a pre-selectedrange of temperature values.
 40. The intelligent battery pack of claim36, further comprising: a battery pack isolation circuit in electricalcommunication with the processor, the battery isolation circuitconfigured to provide a connection signal to the processor indicatingthat the connector of the battery pack is connected to a battery chargeror device to be powered; and wherein the processor responds to theconnection signal by sending a signal to the n-FET to close the n-FET toprovide a voltage across the positive and negative terminals of theconnector.
 41. A battery pack for powering a device, comprising: arechargeable cell having a positive and a negative terminal; a batterypack connector for connecting the battery pack to a charger or a deviceto be powered by the battery pack; a main bus connecting the positiveterminal of the rechargeable cell with a positive connector of thebattery pack connector and also connecting the negative terminal of therechargeable cell with a negative connector of the battery packconnector; and a battery management system in electrical communicationwith the rechargeable cell, including: a processor for monitoring aninput related to the state of charge of the cell, an n-FET disposed inthe front-side bus between the positive terminal of the cell and thepositive connector of the battery pack, the n-FET responsive to a signalgenerated by the processor in response to the input related to the stateof charge of the cell to control the charging or discharging of thecell; a battery pack isolation circuit in electrical communication withthe processor, the battery isolation circuit configured to provide aconnection signal to the processor indicating that the connector of thebattery pack are connected to a battery charger or device to be powered;and wherein the processor responds to the connection signal by sending asignal to the n-FET to close the n-FET to provide a voltage across thepositive and negative terminals of the connector.
 42. The battery packof claim 41, further comprising a boost circuit in electricalcommunication with the n-FET, the boost circuit configured to provide apre-determined bias voltage to a gate of the n-FET to drive the n-FET toconduct a charging current to the first and second rechargeable cells.